The relation of dimer size DNA of the replicative form of the bacterial viruses S13 and phi X174 to genetic recombination is being investigated in continuation of our previous work on this subject. A double-stranded, dimeric intermediate, the "Figure 8", has been identified by electron microscopy that consists of one dimer length and two monomer length single strands. This intermediate is a configuration that allows branch migration to occur. The mechanism by which it is formed and its relation to circular and catenated dimers is being investigated. Related investigations will be made on several bacterial plasmids including the Col El factor from E. coli and a defective Col factor from Shigella dysenteriae. Work is in progress on the transcription of the DNA from Azotobacter vinelandii phage A21 and E. coli phage T4 by the E. coli and A. vinelandii DNA dependent RNA polymerases. This includes study of the basis for the difference between these DNA's with respect to sensitivity of the initiation steps in transcription to KCl concentration and the effect of supercoiling on the translation of circular DNA.